Signaling system



Feb. 18, 1936. McKENzlE COTTRELL.

SIGNALING SYSTEM Filed Deo. 5, 1954 MVR 00 H S Attorney.

Patented Feb. 18, 1936 UNITED STATES SIGrNALINGV SYSTEM McKenzie Cottrell, Stratford, Conn., assigner to General Electric Company, a corporation of New York Application December 5, 1934, Serial No. 756,105

7 Claims.

My invention relates to signaling systems and more particularly to high frequency signal receivers.

In high frequency receivers used in radio re- 5 ception the intensity of the received signals varies over a wide range dependent upon the distance between the receiver and the transmitter from which signals are b-eing received. In such receivers used for both local and distance reception diiiiculty is experienced in obtaining optimum quality of reproduced signal during local reception. If the receiver is to be used fordistance reception it ordinarily includes a number of high frequency amplification stages, which may in- 5 clude radio frequency stages, a frequency converter stage and intermediate frequency stages, thereby to obtain the desired degree of amplification of the received signal and proper selectivity. The use of such a large number of stages, and

particularly the frequency converter stage, re-

duces the quality of reproduced signal obtained, since eachrof these stages introduces a slight amount of distortion.

If such a receiver be used for reception from a. local transmitting station neither the high degree of amplification or the extreme selectivity obtained by a large number of stages is necessary.

Accordingly, it is an object of my invention to 4.provide means whereby certain of said stages may be operatively removed from the receiving circuit during reception of local signals.

A further object of Ymy invention is to provide means whereby the number of stages employed during reception is reduced in responseto the intensity of 'the received signal. A

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in whichFig. 1 represents an ern- 15 bodiment of my invention,` and Figs. 2 and 3 represent certain modifications thereof.

i YReferring to the drawing, I have shown therein a high frequency receiver such as may be used for radio reception which incorporates a pair of antennae I and 2, which may be used for reception of signals of different wave length, and a number of high frequency amplification stages which are conventionally indicated at 3, 4,V and 5. The rectangle 3 may comprise any desired number of radio frequency amplifiers and Ifiliei'edl (Cl. Z50-20) tangle 5 any desired number of intermediate frequency amplifiers, the conventional converter stage 4 being interposed in circuit between these two groups of amplifiers. Rectangle 5 4may also represent any desired equipment for producing 5 unidirectional electromotive force for automatic volume control purposes such as an automatic volume control amplifier and detector, the automatic volume control voltage being supplied to the grids of the controlled stages through the 10 conductors designated A. V. C. conductors on the drawing. Rectangle 6 indicates the usual local electron discharge oscillator having coupled anode and grid coils 'I and 8 which in the arrangement shown are coupled to the input coil 9 i5 of the converterstage 4 and to the output I0 of the radio frequency amplifier 3.

The second detector of the equipment is indicated at I0 and comprises the usual diode, which operates through a low pass filter II into a load 20 resistance I2. Audio `frequency electromotive forces which appear on the load resistanceY I2 may be supplied through audio frequency ampli- 'fiers I3v and I4 and transformer I5 to the input circuits of amplifiers I6 and I'I. The amplifierY II 25 is one adapted particularly for amplification of currents of high audio frequency and supplies these currents through an output transformer I8 to a loudspeaker I9, which is likewise adapted more particularlyv for operation at the high fre- 30 quency range of voice currents. The amplifier I6 is one designed for operation over the entire j voice frequency range but which is not so faithful in its operation at the high audio frequencies as the amplifier I'I. Signals supplied through 35 amplifier I6 are reproduced by a loudspeaker 20,

which is one adapted more particularly for reproduction of the greater portion of the voice frequency band but the operation of which'is less faithful in the high frequency range than the 40 loudspeaker I9.

In the upper portion of the drawing are shown a number of switches 2l, 22, 23, 24, 25, 26, 21, 28,

` 29 which are mechanically connected together for wave reception and for high selectivity. Signals 55 received upon the antenna 2 are amplified in the amplifier 3 supplied through transformer 9, I0 to the input of the first detector 4. In this input circuit the signals are mixed with the oscillations from the local oscillator 6 to produce in the output circuit of the detector 4 currents of the desired intermediate frequency, which may be the difference frequency between the received oscillations and the oscillations of the source 6. These oscillations are amplified in the intermediate frequency amplifier 5 and rectified by the detector I9', the audio frequency oscillations appearing upon the load resistor I2. These oscillations are amplified by the amplifiers I3, I4, and I6 and the received signals reproduced by the loudspeaker 20. Thus in this position of the fidelity-selectivity control means the receiver has the high selectivity and high amplification afforded by the large number of stages as well as by the superheterodyne action obtained through the converter stage. The signals reproduced, however, are not of maximum fidelity by reason of the presence of the large number of stages.

In this position of the selectivity-delity control switches the loudspeaker I9 is short circuited by the switch 29, and accordingly, the high frequency voice currents are reproduced only to the extent of the capabilities of loudspeaker 20. This is desirable in order to eliminate heterodyne squeals when the tuning control is adjusted to positions between stations due to the crowded condition of the broadcast frequency spectrum, and alsoY to reduce, or eliminate, static noises where the receiver has high sensitivity. Accordingly, loudspeaker I9 is effectively removed from the circuit. In addition, these currents may be attenuated by the reactor 3l, which is in series with the output of audio amplifier I3, and condenser 32. The effectiveness of this latter condenser may be varied by means of the rheostat 33 whereby the amount of high frequency voice currents vtransmitted through the amplifier may be varied for tone control purposes.

Condenser 32 may also be employed for reduction of the high frequency audio currents. This condenser is connected across the input to the audio amplifier through a variable resistance 33' the movable element of which is mechanically connected with the movable element of ypotentiometer I2 thereby to reduce the resistance 33 as the volume is reduced. This, in turn, renders the condenser 32' more effective at low volumes of signal. This arrangement is described with greater particular-ity and claimed in copending application Serial No. 31,274, filed July 13, 1935 by Walter H. Nelson and entitled Combined volume and bass tone compensation control device, which application is assigned to the same assignee as my present application.

If it be desired to receive long waves switches 30 may be moved to their lower position thereby to connect antenna I to the receiver. 1 n

In the illustrated position the input to direct current amplifier 44 is connected across load resistance I2. This amplifier may include in its output circuit a meter 43 which may be employed for accurate tuning of the receiver.

When the switches 2|, 22-29 are operated to their intermediate positions the local oscillator 6 becomes deenergized by action of the switch 24. Switch 23 also applies a positive potential to the cathode of converter 4 thereby making the grid negative with respect to the cathode and rendering this stage completely inoperative even at high R. F. signal levels. By means of switches 22 and 25, the detector I0 is disconnected from the intermediate frequency amplifier and is connected directly to the coil 9, which in turn is coupled to the coil I0. 'I'hus radio frequency signals are supplied directly from the radio frequency amplifier to the detector I 0, the converter stage and intermediate frequency amplifier stage 5 being effectively removed from the circuit. At the same time audio frequency amplifier I3 and the tone control network 3|, 32, 33 are removed from the circuit by switches 2I and 28, the variable contact on potentiometer I2 being now connected directly to the input of audio amplifier I4. In this position, the short circuit about the loudspeaker I9 is removed by the switch 29 and by means of switch 26 the input to direct current amplifier 44 is now connected to an intermediate point on resistance I2. The purpose of this is to obtain approximately equal input to the direct current amplifier in both positions of the switch. L"

The apparatus is now adapted for reception of strong signals from local stations to obtain the maximum fidelity of reproduction possible and produces a maximum of fidelity. It, of course,

now operates without automatic volume control since after the equipment 4, 5 and 6 is disabled, no variable automatic volume control voltage is produced and the bias on the radio frequency amplifiers becomes constant.

When the switches 2|, 22-29 are moved to the right all of the high frequency circuits are removed and the input to the amplifier I3 is connected to phonograph equipment 34 for reproduction of recorded signals. In this condition of the equipment the loudspeaker I9 is again :L

short circuited thereby to reduce the reproduction of high frequency currents to avoid record scratching sounds.

In Figs. 2 and 3 I have shown modifications of my invention whereby the change from the high selectivity Vcondition to the high fidelity condition and vice versa may be effected automatically. In Fig. 2 I have conventionally indicated switches 2l to 29 as being operated by corresponding electromagnets 2| to 29', the latter being Vconnected in a series circuit which, of course, includes an electromagnet for` each of the switches shown in Fig. 1 as indicated by the portions thereof which are dotted. This circuit is controlled by a relay 35 which in turn is supi plied with direct current from a direct current amplifier 36. The latter includes in its grid circuit a resistance 3l which in turn is connected between the anode and cathode of a diode 38.

The diode is energized from a radio frequency electromotive force which may, if desired, be amplified by a radio frequency amplifier 39 derived from any suitable portion of the radio frequency circuit. For example, the amplifier 39 may have input terminals 4U connected at then: Vterminals 4I of the circuit shown in Fig. 1.

selectivity tothe high fidelity condition exactly as described in connection with Fig'V 1.

Fig. 3 differs from Fig. 2 principally in that in place of the various electromagnets 2|'29' a single electromagnet 42 is employed to operate the various switches 2|-29, otherwise the circuit of Fig. 3 diifers from Fig. 2 only-with respect to the type of bias means employed on the cathode of discharge device 29.

While I have shown particular embodiments of my invention it will of course be understood that I do not wish to be limited thereto since different modifications may be made both in the circuit arrangement and in the instrumentalities employed. I of course contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of 'my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination, in a high frequency receiver, of .an input circuit, means for converting high frequency currents received in said receiver to currents of different frequency, signal means responsive to said currents of different frequency, and means to disable said first means and to connect said input circuit'to said signal means.

2. The combination, in a high frequency receiver, of an input circuit, means for converting high frequency currents received in said receiver to currents of different frequency, means to demodulate said currents of different frequency, a sound reproducing device responsive to the products of said demodulation, and means to disconnect said first means from said detector and to connect said detector to said input circuit.

3. The combination, in a high frequency re- Y ceiver, of an input circuit, a sound reproducing device, .a plurality of high frequency amplification stages, a detector and a plurality of low frequency amplification stages interposed between said input circuit and said sound reproducing device, switching means to disconnect said detector from the output of one of said stages and connecting it to another stage, switching means to change the number of .audio stages between said detector and said sound producing device, and means to operate said switching means simultaneously.

4. The combination, in a high frequency receiver, of an input circuit, a sound reproducing device, a frequency converter stage and a detectcr stage between said input circuit and said sound reproducing device, and means to disable said converter stage and to connect said detector stage to said input circuit.

5. The combination, in a high frequency receiver, of an input circuit, and a plurality of sound reproducing devices, said sound reproducing devices being adapted for operation over different frequency ranges, .a plurality of amplification stages interposed in circuit between said input circuit and said sound reproducing devices, and switching means whereby certain of said amplification stages may be removed from and restored to said circuit, means whereby one of said sound reproducing devices is operatively disconnected from said circuit and restored thereto, .and means to operate said last two means to disconnect said certain amplification stages from said circuit and to restore said one sound reproducing device to said circuit simultaneously.

6. The combination, in a high frequency re- 5 

